Devices and methods for feedthrough leakage current detection and decontamination in ionization gauges

Abstract

Devices and corresponding methods can be provided to test an ionization gauge, such as a hot cathode ionization gauge, for leakage currents and to respond to the leakage currents to improve pressure measurement accuracy. Responding to the leakage current can include applying a correction to a pressure measurement signal generated by the gauge based on the leakage current. Responding to the leakage current can also include removing contamination causing the leakage current, where the contamination is on electrical feedthrough insulators or other gauge surfaces. Testing and correcting for leakage currents and removing contamination can be completed with the ionization pressure gauge in situ in its environment of use, and while the gauge remains under vacuum.

What is claimed is: 
     
       1. A device comprising:
 an ionization gauge in which ions are generated by electron flow between a cathode and an anode; and 
 an electrical circuit coupled to the ionization gauge and configured to test the ionization gauge under vacuum in situ for leakage current and to respond to the leakage current to improve pressure measurement accuracy by applying a correction for the leakage current in an electron emission current control feedback loop that is configured to control the electron flow between the cathode and the anode. 
 
     
     
       2. The device of  claim 1 , wherein the electrical circuit is further configured to decontaminate the ionization gauge in situ by electrically heating contamination in the ionization gauge. 
     
     
       3. The device of  claim 2 , wherein the electrical circuit is further configured to decontaminate the ionization gauge with the ionization gauge under vacuum. 
     
     
       4. The device of  claim 2 , wherein the contamination is on an electrical insulator configured to electrically isolate an electrical feedthrough conductor in the ionization gauge, and wherein the electrical circuit is further configured to electrically heat the contamination by increasing a voltage across the electrical feedthrough insulator to increase any current passing through the contamination on the insulator. 
     
     
       5. The device of  claim 1 , wherein the tested leakage current is from at least a cathode feedthrough conductor. 
     
     
       6. The device of  claim 1 , wherein the tested leakage current is from at least an anode feedthrough conductor. 
     
     
       7. The device of  claim 1 , wherein the electrical circuit is further configured to respond to the tested leakage current by applying a correction to a pressure measurement signal generated by the device based on the leakage current. 
     
     
       8. The device of  claim 1 , wherein the electrical circuit includes a current sensor configured to measure a calibration current that reflects leakage current and to measure electron emission current and a processor to compute pressure based on the calibration current and the measured electron emission current. 
     
     
       9. The device of  claim 1 , wherein the electrical circuit is configured to test for the leakage current by increasing voltage applied across an electrical feedthrough insulator and measuring current through the contamination on the insulator. 
     
     
       10. The device of  claim 1 , wherein the ionization gauge is a hot cathode ionization gauge. 
     
     
       11. The device of  claim 1 , further including an indicator configured to provide, based on a level of the tested leakage current, an indication that the ionization gauge requires service or replacement. 
     
     
       12. The device of  claim 1 , wherein the measured vacuum pressure has an accuracy within a range of about ±15% when the ionization gauge is operated with an electron emission current in a range of about 5-10 microamperes. 
     
     
       13. A method comprising:
 measuring vacuum pressure in an ionization gauge by measuring ions generated with electron flow between a cathode and an anode; 
 testing the ionization gauge under vacuum in situ for leakage current; and 
 responding to the leakage current to improve pressure measurement accuracy by applying a correction for the leakage current in an electron emission current control feedback loop that is configured to control the electron flow between the cathode and the anode. 
 
     
     
       14. The method of  claim 13 , wherein pressure measurement accuracy is further improved by decontaminating the ionization gauge in situ by electrically heating contamination in the ionization gauge. 
     
     
       15. The method of  claim 14 , wherein decontaminating the ionization gauge is performed with the ionization gauge under vacuum. 
     
     
       16. The method of  claim 14 , wherein the contamination is on an electrical feedthrough insulator configured to electrically isolate an electrical feedthrough conductor in the ionization gauge, and wherein electrically heating the contamination comprises increasing a voltage across the electrical feedthrough insulator to increase any current passing through the contamination on the insulator. 
     
     
       17. The method of  claim 13 , wherein the tested leakage current is from at least a cathode feedthrough conductor. 
     
     
       18. The method of  claim 13 , wherein the tested leakage current is from at least an anode feedthrough conductor. 
     
     
       19. The method of  claim 13 , wherein responding to the leakage current further comprises applying a correction to the pressure measurement based on the tested leakage current. 
     
     
       20. The method of  claim 13 , wherein measuring vacuum pressure includes measuring electron emission current using a current sensor, testing for leakage current includes measuring, using the current sensor, a calibration current, and responding to the leakage current includes calculating pressure based on measured electron emission current and the calibration current. 
     
     
       21. The method of  claim 13 , wherein testing for leakage current comprises increasing voltage applied across an electrical feedthrough insulator and measuring current through the contamination on the insulator. 
     
     
       22. The method of  claim 13 , wherein the ionization gauge is a hot cathode ionization gauge. 
     
     
       23. The method of  claim 13 , further comprising providing, based on a level of the leakage current, an indication that the ionization gauge requires service or replacement. 
     
     
       24. The method of  claim 13 , wherein the measured vacuum pressure has an accuracy within a range of about ±15% when the ionization gauge is operated with an electron emission current in a range of about 5-10 microamperes.